I actually did buy one of the best (and expensive) fitted car covers for the Crossfire. However, they will tell you there isn't anything completely waterproof, water will get beyond the car cover if it rains enough, either directly or due to condensation build up.

The problem is the old paint on these cars are usually very porous. What will happen is that the water that is trapped under the cover, if enough of it, will stain the paint, sometimes permanently if it gets deep enough.

I found that out the hard way last year. Luckily only one small area was stained enough to require repaint, the rest was buffed off. I do use the cover during the heat of the summer, great way to protect the paint.